Blade elements provided for improving the efficiency and for changing the aerodynamic profile of a wind turbine rotor blade and such elements mounted to a trailing edge of a blade are well known from patent literature. Example hereof are EP 1 314 885 B, EP 2 195 525 A, WO 2009/026929 A1, EP 2 031 242 A1, US 2010/143151 A, EP 1 775 464 A and U.S. Pat. No. 5,328,329 A. The elementary features like normal elastic trailing edge or serrated edge are also much known from the cited literature.
In US 2010/0143151 A1 a wind turbine blade is disclosed, which includes a permeable flap extending from a trailing edge of the blade. The flap can be retrofit to existing blades and may flush with the outer surface of the blade.
In U.S. Pat. No. 5,328,329 a width extender is provided, which is used to modify existing fan blades in order to enable them to rotate at slower speed thereby reducing the noise associated with them while at the same time maintaining proper work efficiency. The width extender is fixably connected along the trailing edge of an existing fan blade by, for example, adhesive bonding.
In EP 2 195 525 A, WO 2009/026929 A1 and EP 2 031 242 A1 a blade element for mounting on a wind turbine blade is provided. The blade element has a shape so that, by mounting in a first longitudinal part of the wind turbine blade, it changes the profile of the first longitudinal part from the first airfoil profile with an essentially pointed trailing edge and a first chord length to a changed airfoil profile with a blunt trailing edge. The changed airfoil profile is a truncated profile of an imaginary airfoil profile with an essentially pointed trailing edge and a second chord length which is larger than the first chord length.
In EP 1 775 464 A2 a wind turbine with a blade rotor which reduces noise by the inclusion of a set of flexible bristles is disclosed. The set of flexible bristles is aligned in at least one row on the trailing edge of the aerodynamic profile of the blade and protrudes over it.
In EP 1 314 885 B1 a method and an apparatus for improving the efficiency of a wind turbine rotor are disclosed. The wind turbine rotor comprises a serrated panel connected to each wind turbine rotor blade, an upper and a lower surface on each panel, a plurality of span-wise, periodic indentations on each panel, means for connecting the serrated panel to a trailing edge on each of the wind turbine rotor blades of the wind turbine rotor such that the serrated panel extends from the trailing edge into airflow behind the trailing edge. The serrations on each wind turbine rotor blade have an angle different from 0° relative to a mounting surface on each of the wind turbine rotor blades. The serrations on each of the serrated panels have a given stiffness allowing for an angle of the serrations to change passively in response to speed and angle of the airflow at the trailing edge of each of the wind turbine rotor blades due to flexing of the serrations and the serrated panel.